MLA
McAnally, D. R. (David Rice), 1810-1895. Letter from D. R. McAnally (St. Louis, Missouri) to Robert Paine - April 4, 1853. April 4, 1853. Robert Paine Papers, 1828-1882. Pitts Theology Library. https://digital.library.emory.edu/purl/798mcvdpkc-cor.
APA, 6th edition
McAnally, D. R. (David Rice), 1810-1895. (April 4, 1853)[Letter from D. R. McAnally (St. Louis, Missouri) to Robert Paine - April 4, 1853]. Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/798mcvdpkc-cor.
Chicago
McAnally, D. R. (David Rice), 1810-1895, Letter from D. R. McAnally (St. Louis, Missouri) to Robert Paine - April 4, 1853, April 4, 1853, Robert Paine Papers, 1828-1882, Pitts Theology Library. https://digital.library.emory.edu/purl/798mcvdpkc-cor.